Variable-delivery multi-stage hydraulic pumps



sept, 12, 1961 A. CAMERON-JOHNSON VARIABLE-DELIVERY MULTIV-STAGE HYDRAULIC PUMPS Filed Sept. 4, 1958 4 Sheets-Sheet 1 um ma www um kwak Nq E. W nw www QN /Nmr l wm ...I N l||. 1 l... 1 T11 Y ww l/ Nlx L NW\\ @ma .BNQ NN@ @www @ww A Unk Sept- 12, 1961 AA. :,\M|5|=zo1\1'.1oHNsoN 2,999,463

VARIABLE-DELIVERY MULTI-STAGE HYDRAULIC PUMPS 4 Sheets-Sheel 2 Filed Sept. 4, 1958 Sept 12, 1951 A. cAMERoN-JoHNsoN 2,999,463

VARIABLE-DELIVERY MULTI-STAGE HYDRAULIC PUMPS 4 Sheets-Sheet 3 Filed Sept. 45 1958 Sept 12, 1961 A. CAMERON-JOHNSON 2,999,453

VARIABLE-DELIVERY MULTI-STAGE HYDRULIC PUMPS 4 Sheets-Sheet 4 2,999,463 VARIABLE-DELIVERY MULTI-STAGE HYDRAULIC PUMPS Alan Cameron-Johnson, Gloucester, England, assignor to Rotol Limited, Gloucester, England, a British company Filed Sept. 4, 1958, Ser. No. 759,072 Claims priority, application Great Britain Sept. 11, 1957 11 Claims. (Cl. 10B- 5) This invention relates to variable delivery multi-stage hydraulic pumps, and is concerned with such pumps in which the final stage is of the positive displacement type.

It is desirable to provide in such pumps means which enable the nal pump stage to be off-loaded progressively as the pump delivery pressure increases.

Further it is desirable to provide in these pumps additional means operative to effect off-loading of the priming pump means simultaneously with oft-loading of the final stage of the pump.

` According to the invention a Variable delivery multistage hydraulic pump unit comprises in combination, a positive displacement pump having a fluid inlet and a iluid outlet, a non-positive displacement pump for priming said positive displacement pump and also having a uid inlet and a fluid outlet, conduit means connecting the iluid outlet of the priming pump with the iluid inlet of the positive displacement pump, valve means in the conduit means and a piston means in operative connection with the valve means which piston means is connected to be loaded by the delivery pressure of the unit and is arranged to cause the valve means to throttle the conduit on increase of the delivery pressure of the unit. Preferably the` positive displacement pump is a swash plate type piston pump, and the priming pump is ya centrifugal flow pump.

All stages of such a pump unit may be powered by means of a common drive shaft connected to a power source which may in the case of gas turbines, or electric motors be rotating up to 10,000 to 12,000 r.p.m.

Further the piston means may be conveniently arranged to operate additionally as a high pressure relief valve for the swashplate type pump.

The priming pump means may be provided with further valve means arranged to enable the off-loading of the priming pump means to take place simultaneously with the oit-loading of said sw-ashplate type pump.

Thevalve means may be adapted and connected to be biased towards its closed position by the pressure diiierential across the priming pump.

A convenient type of valve means is in the form of a spool valve having at one end `a dilerential piston, the spool valve being movable within the main cylinder and the differential piston being movable within the auxiliary cylinder, the spool valve having an internal passage which opens on one side of the piston and is arranged for fluid connection with the outlet of said priming pump, the auxiliary cylinder having an opening to the space bounded by the auxiliary cylinder walls and a face of the piston remote from the internal passage opening, which opening in the auxiliary cylinder puts the auxiliary cylinder in iluid connection with the inlet of the priming pump.

An alternative valve means includes a spool valve reciprocable within the cylinder hollow stem integral withl Sagewey ,which is boundedrartltbylhe fafa@ o? wensten.

" nited States Patent Ice remote from the cylinder being in uid connection with the outlet of the priming pump.

In a pump according to the invention, the valve means in the conduit means may have a bleed passage preferabll having a constriction therein for maintaining uid connection between the priming pump outlet and the positive displacement pump inlet even when the valve means is fully obstructive.

A number of embodiments of the invention will now be described by way of example with reference to the accompanying diagrammatic drawings, in which FIGURE l shows a two-stage pump of the invention, in its simplest form,

FIGURE 2 shows another two-stage pump which, additionally to the construction of FIGURE 1, incorporates oit-loading means for the priming pump stage,

FIGURE 3 shows a further two-stage pump similar in construction to the pump of FIGURE 2 which incorporates pressure biasing means on the throttle valve and FIGURE 4 shows yet another two-stage pump which incorporates an alternative arrangement for pressure biasing of the throttle valve.

Referring now to FIGURE l, a pump of the invention comprises a casing 11 having a number of longitudinally directed internal bores 12 which extend along a part of the length of the pump, yand are arranged on the circumference of a cylinder having the axis of the pump as its centre. These bores 12 contain plungers or pistons 13 reciprocable therein, each plunger having a part-spherical seating 14 incorporated integrally at its right-hand end when viewed as in the drawing. Only one of these plungers is shown. Universally mounted in each seating 14 is a semi-spherical pad 15 having an integral circular thrust face 16. The faces 16 bear on a swashplate member 17 which is mounted for rotation about the longitudinal axis of the pump, and is journalled in bearings 18 and 19. An integral swashplate spindle 20 projects through the end wall of the pump casing and carries a set of splines 21 for engagement with a quill shaft taken from a prime mover (not shown). A retaining plate 22 having a hemi-spherical centre mounting 23 is universally mounted in a hemispherical seating 24 in the middle core 25 of the pump casing 11. The centre of the retaining -plate 22 lies on the longitudinal axis of the pump, and the plate 2.2 which may be spider-like in shape, engages a collar 26 beneath the seating 14 of each plunger 13 to hold the thrust faces 16 in engagement with the working face of the swashplate 17.

The middle core 25 of the casing 11 incorporates an inlet chamber 27 for the swashplate type pump, and galleries such as shown at 28 are taken from this chamber 27 to an annular chamber 29 which forms annular ports around the bores or cylinders 12, approximately midway along their length. Each bore 12 opens at its lefthand end (when viewed as in FIGURE l) into an annular delivery chamber 30. A non-return plate valve 31 is provided at the opening of each bore into chamber 30 and is urged to the closed position by means of a coil spring 32. The delivery chamber 30 opens into a 4delivery connection 33 and hence out of the pump.

The inlet chamber 27 is connected by means of a passageway 34 to a bore 35, the longitudinal axis of which is disposed at right angles to that of the pump. The bore 35 is at step 36 increased in diameter towards its upper end as shown in the drawing to form a spring chamber 37. The bore 3S accommodates a spool valve 38 having lands 39 and 40 provided thereon. A passageway 41 communicates the bore 35 with an annular outlet duct 42 surrounding a centrifugal pump rotor or impeller 43. The rotor 43 is mounted for rotation in av suitable bearing `44, retained;u atthe left-hand endof the.

pump casing 11. The centrifugal pump rotor 43 may be directly connected with the spindle of the swashplate 1n convenient manner. An inlet passageway 45 is provided in the pump casing, which passageway leads to the eye of the rotor 43.

The spool Valve 38 is provided with a passageway 46 therethrough this passageway 46 having a restriction or throat at 47. In the drawing the spool valve is shown in the lower position in which position it is open, being urged to this position by means of a double coil spring arrangement 48 which bears on a ianged plate 49 connected to the spool valve. It will be seen that the passageway 46 is arranged so that when the valve 38 is closed, a bleed of hydraulic liuid is permitted -to pass from the passageway 41 through the restriction 47 into the passageway 34.

A passageway 50 is taken from the delivery chamber 30 to the underside of a piston 51. The lower end of the piston 51 is stepped at 51a to provide a portion 52 o-f smaller diameter, and the upper end of piston 51 is in engagement with the lower face of the spool valve 38. A passageway 53 places the spring chamber 37 in com* munication with a chamber 54 surrounding the swashplate. A further passageway 55 places a chamber 56 formed in the bore 3-5 on the underside of the spool valve 38 in communication with the passageway 53. A small annulus 57 formed in the pump casing around the piston 51 approximately midway along its length is also in communication with the passageway S3 through a passageway 58. This small annulus and the piston 51 form a high pressure relief valve for the pump.

A connection 59 is taken from the swashplate chamber 54 to tank (not shown). A lightly loaded relief valve 66 is provided at this connection.

The operation of the pump described above is as follows: When not under load, thrust faces 16 are held in contact with the swashplate 17 by the nutating retaining plate 22. Hydraulic fluid, having entered the cylinders 12 from the inlet chamber 27 when the annular ports 29 in the walls of the cylinders are uncovered by the pistons at the outer end of their travel, is discharged to delivery by the plungers 13 through non-return valves 31. Supply to the ports 29 is from the centrifugal pump 43, via the annulus 42, the passageway 41, the annulus formed in the piston valve 38 between the lands 39` and 40, the passageway 34, the chamber 27 and the galleries 28. Under normal conditions the throttle or spool valve 38 is held open by the spring assembly 48.

From the high pressure delivery chamber 30 fluid is passed through the passageway 50 to act upon the annular area of the piston 51 afforded by the step 51a. The piston size and the spring assembly are designed so that as the fluid pressure increases above a selected value less than the designed maximum, the valve is caused to move progressively towards a fully obstructive position. At maximum pressure, the throttle valve is in the fully obstructive position and a small quantity of fluid only is allowed to pass through the metering restriction 47 to maintain system pressure and permit lubrication and cooling of the pump. Any excess fluid is relieved past the step 51a of the piston 51 into the passageway 58, from which it returns via the swashplate chamber 54 and relief valve 60 to tank. Since the pump is of the wet casing type, complete fullness of the casing is ensured by means of the relief valve 60, the pressure differential being suicient to retain the head of fluid at normal accelerations yduring operation.

Referring now to FIGURE 2, the construction illustrated is similar to the construction of FIGURE 1, and like pants have the same numerical references. The construction diifers, however, in that an additional valve 61 is incorporated in a passageway 62 leading from passage- Way 41 back to the centrifugal pump inlet 45 and prevents communicaton between the passageways 41 and 62. Further a constriction 63 is incorporated in a passageway 64 taken from passageway 41 from the centrifugal pump outlet duct 42.

Passageway 64 communicates with the underside of the valve 61 which presents a larger pressure area than is under pressure from passageway 41. A spring 65 urges the valve 61 on to its seat. A passageway 66 is taken from the passageway 64 to the lower end of the bore 35, in which valve 38 reciprocates, and passageway 66 is arranged so `that when the spool valve 38 is in its open position, the end of the passageway 66 is blanked olf. When however, the valve 38 is lifted, communication of the passageway 66 with the bore 35 occurs. The bore 35 in this construction opens into a passageway 67 which leads into the inlet passage 45 to the centrifugal pump 43.

The only other difference between this construction and that of FIGURE 1, is that the metering restriction o-r throat 47 is incorporated in a passageway 68 which always communicates passageway 41 with the -annulus formed between lands 39 and 40'.

The purpose of the additional valve 61 is to olf-load the priming pump by providing return circulation to inlet when the main high pressure pump is off-loaded.

The centrifugal pump is inherently a variable delivery type, in which fluid ow and pressure are related according to the characteristic of the particular unit, it being possible to stall the pump at some relatively high pressure without structural damage and without the need of a relief valve. Pump pressure increases substantially as the speed squared, a characteristic similar to the pressure drop of iluid through the various orifices elsewhere in the pump unit, and at speeds in the order of 10,000 to 12,000 r.p.m. at which operation of this pump is proposed, the

pressure available from the centrifugal pump is of useful magnitude.

It has been found desirable not to stall the centrifugal pump completely, since Vibration of the impeller blades has been known to occur under these conditions and it is for this reason that the additional valve 61 is provided. This valve is normally held closed on to its seating by virtue of unbalanced areas, pressure to the larger side being fed through the constriction 63 and the resultant load supplemented by the coil spring 65. Flow from the underside of the valve 61 is prevented by the open throttle valve 38 when the pump is operating normally, and the additional valve `61 is closed. When the pump is olloaded however, the throttle valve, in moving upwardly uncovers the end of the passageway 66 and the resultant pressure drop across the constriction 63 permits opening of the valve 61 by virtue of the pressure dilferential across it. Thus at a pressure determined by the valve spring 65 a proportion of the flow from the centrifugal pump 43 is re-circulated. This maintenance of flow through the impeller is material in assisting quick response of the pump coming on-load.

The inter-stage pressure, that is the pressure between the centrifugal pump 43 and the swashplate type pump, is a function of pump speed and inlet pressure, and the flow through the throttle valve 38 at any position will vary correspondingly. This would result in changes of the pressure ow characteristic, with changes in these two variables.

To compensate to some extent, it may be desirable tov render the piston and valve assembly lsensitive to the pressure differential across the rotor 43 in order to give the required bias against the spring assembly 48.

FIGURE 3 shows a construction in which the above compensation is achieved.

Accordingly the spool valve 38 is provided with an internal bore 69 closed at its lower end and extending at its upper end through a stem-like extension 70 of the valve, the latter terminating in a differential piston 71. The differential piston 71 can reciprocate within an auxiliary cylinder 72. 'I'he bore 69 opens to the underside of the differential piston 7'1, while the upper face of the diierential piston 71 is in communication with the inlet passageway 45 through a passageway 73 and the passageway 67. The bore 69 is always in communication with the passageway 41 and thus receives delivery pressure fluid from the centrifugal pump. It will be seen that in this construction the restriction or throat 47 is incorporated in the wall of the spool valve between the lands 39 and 40. Another diiference between this construction and that off FIGURE 2, is that there is no passageway equivalent to passageway 64 and the constriction or throat 63 is incorporated in the head of the valve 61.

From this construction it will be seen that the bias of the pressure differential across the centrifugal pump is simply applied to the spool Valve in opposition to the effort of the spring assembly 48. Strictly speaking, for true compensation the bias should operate with respect to absolute zero pressure, but this is not the case with the present arrangement since the inlet to the centrifugal pump is pressurized by some external means which might well be considered in effect an additional pump stage. However, the arrangement shown is considered precise enough for the maintenance of a reasonably consistent performance curve.

FIGURE 4 shows yet a further construction in which the diterential pressure bias is applied to the throttle valve in a still more practical manner.

In this case both lower and upper ends of the throttle valve y38 are subjected to centrifugal pump inlet pressure through passageway 67 and a passageway 74, While the compensating means for inter-stage pressure is now located wholly within the throttle valve.

A hollow stem 75 coaxial with the longitudinal axis of the valve and integral with the pump casing extends through the bore 69 of the throttle valve 38. The stem 75 incorporates a piston 76 at its lower end, about which piston 76 the throttle valve 38 is reciprocable. Hydraulic fluid at inlet pressure passes through a port 77 at the upper end of the stem into the hollow interior 78 thereof, thereafter passing to the underside of the piston 76. Hydraulic fluid under pressure from the centrifugal pump outlet passes from passageway 41 and through a passageway 38a in the wall of valve 3-8 to the interior thereof above the piston 76. In this way the throttle valve 38 is given a diiferential pressure bias in the upward direction against the spring assembly. By so locating the compensator arrangement, structural and functional advantages are obtained. These are, for example, the avoidance of an external or additional connection from the compensator to the inlet manifold, and the fact that the compensator can be made self-aligning in the valve. The compensator may be used as a throttle valve damper.

In the previous constructions the swashplate is lubricated and cooled by leakage from the throttle valve, and leakage past the high pressure plungers. ln certain practical applications, such leakage is not likely lto provide adequate flow through the pump casing to dissipate generated heat. In the construction of FIGURE 4 a positive supply of uid is provided under all conditions. An additional constriction 79 in the throttle valve 33 meters rst-stage pressure uid through a passageway 80 and the passageway 53 into the swashplate chamber 54, except when the pump is olf-load. Under oi-load conditions the bleed through the constriction 79 is cutolf by upward movement of the valve 38 and system make-up flow into the swashplate chamber 54 occurs through the high pressure relief valve formed by the piston 51 and small annulus 57, and through passageways SS and 53. As before, casing pressure and hydraulic fullness are maintained by the relief valve 60 and the by-pass connection 59.

I claim:

l. A variable delivery multi-stage hydraulic pump unit comprising in combination, a positive displacement pump having a uid inlet and a fluid outlet, a non-positive displacement pump for priming said positive displacement pump and also having a uid inlet and a iluid outlet, conduit means connecting the fluid outlet of the priming pump with the iluid inlet of the positive displacement pump, valve means in the conduit means, a piston means in operative connection with the valve means which piston means is connected to be loaded by the delivery pressure of the unit and is arranged to cause the valve means to throttle the conduit on increase of the delivery pressure of the unit and biasing means subjected to loading in dependence upon the difference in pressure at the inlet and outlet of the priming pump, which biasing means is in operative connection with the valve means to bias the valve means to throttle the conduit.

2. A pump unit as claimed in claim l wherein the positive displacement pump is a swash plate type piston pump, and the priming pump is a centrifugal ow pump.

3. A pump unit as claimed in claim l wherein all stages of the pump unit are powered by means of a common drive shaft connected to a power source.

4. A pump unit as claimed in claim l wherein the piston means is arranged to operate additionally as a high pressure lrelief valve for the positive displacement pump.

5. A pump unit as claimed in claim l wherein the priming pump means is provided with further valve means arranged to enable recirculation of part of the delivery of the priming pump means -to take place simultaneously with the off-loading of said positive displacement pump.

6. A pump unit as claimed in claim l further comprising a main cylinder in the conduit means and an auxiliary cylinder in fluid connection with Vthe inlet of the priming pump, wherein the valve means is in the form of a spool valve having at one end a diierential piston, the spool valve being movable Within the main cylinder and the diiferential piston being movable within the auxiliary cylinder, the spool valve having an internal passage which opens on one side of the piston and is arranged for uid connection with the outlet of said priming pump, the auxiliary cylinder having an opening to the space bounded by theauxiliary cylinder walls and a face of the piston remote from the internal passage opening, which opening in the auxiliary cylinder puts the auxiliary cylinder in fluid connection with the inlet of the priming pump.

7. A pump unit as claimed in claim l further comprising a cylinder in the conduit means wherein the valve means includes a spool valve reciprocable within the cylinder, an internal passageway in the spool valve, a hollow stem integral with the pump casing extending into the internal passageway and terminating in a piston located in a cylinder provided by the internal passageway of the spool valve, the hollow stem being in fluid connection with the inlet to the priming pump and openning into the cylinder provided by the internal passageway, and the space in the internal passageway which is bounded partly by the face of the piston remote from the cylinder being in uid connection with the outlet of the priming pump.

8. A pump unit as claimed in claim 1 wherein the valve means in the conduit means has a bleed passage for maintaining Huid connection between the priming pump outlet and the positive displacement pump inlet even when the valve means is fully obstructive.

9. A pump unit as claimed in claim 8 wherein the bleed passage has a constriction therein.

lO. In a pump unit comprising a fluid inlet and a iiuid outlet, a non-positive displacement priming pump the the uid inlet of which is in uid connection with the unit fluid inlet, a positive displacement delivery pump the fluid outlet of which is in fluid connection with the unit iuid outlet, a main cylinder, a first conduit connecting the iiuid outlet of the priming pump to the main cylinder, a second conduit connecting the main cylinder to the delivery pump fluid inlet, and an auxiliary cylinder connected at one end thereof to the unit fluid inlet, valve means to control communication between the first conduit and the second conduit in the form of a spool valve having at one end thereof piston means arranged to be loaded by the delivery pressure of the unit and arranged to cause the spool valve to throttle the connection between the first and second conduits, and at the other end thereof a differential piston, the spool valve being slidable in the main cylinder and the dierential piston being siidable in the auxiliary cylinder, said spool valve having a passage therein, said passage opening at one end for connection with the first conduit and at the other end on the side of the differential piston in the auxiliary cylinder remote from the inlet to the auxiliary cylinder.

11. In a pump unit comprising a pump casing, a fluid inlet and a fluid outlet, a non-positive displacement priming pump, the fluid inlet of which is in fluid connection with the unit lluid inlet, a positive displacement delivery pump the iluid outlet of which is in lluid connection with unit uid outlet, a cylinder, a first conduit connecting the priming pump outlet with the cylinder, a second conduit connecting the cylinder with the delivery pump inlet and 20 a third conduit connecting the unit fluid inlet with the cylinder; valve means to control the connection between the first and second conduits including a spool valve reciprocable within the cylinder, piston means in operative connection with said spool valve arranged to be loaded by the delivery pressure of the unit and to cause the spool valve to throttle the connection between the lirst and. second conduits, an inner cylinder within the spool valve, a stem integral with the pump casing and extending into the inner cylinder, a piston at the free end of the stem, said piston working in the inner cylinder, said stem having a passageway therein opening at one end into the inner cylinder at the piston face and at the other end at a positionV to be in fluid connection with the third conduit, the space in the inner cylinder bounded partly by the piston part remote from the piston face being in luid connection with the first conduit.

References Cited in the iile of this patent UNITED STATES PATENTS 2,295,833 Deschamps Sept. l5, 1942 2,337,821 Huber Dec. 28, 1943 2,365,309 Talbot Dec. 19, 1944 2,642,804 Bowers .Tune 23, 1953 2,643,612 Westbury June 30, 1953 2,653,543 Mott Sept. 29, 1953 2,780,170 Stoyke `et al. Feb. 5, 19,57 

